The present invention relates generally to power line communication systems and, more specifically, to portable meter reading apparatus that is able to be connected to the power line at a location that is remote from the meter that is to be read.
For many years, electric utility companies have measured the consumption of electrical energy, by their customers, with the use of electromechanical kilowatthour meters. A typical kilowatthour meter contains a plurality of dial indicators that represent the digits of a cumulative electrical energy consumption for the residence to which the meter is connected. In order to determine the monthly energy usage for each of the utilities' customers, the cumulative value of electrical energy consumption represented by the meter register is manually read and recorded on a monthly or bi-monthly basis. The energy used during the billing period can then easily be determined by comparing the cumulative values for successive periods. This type of meter reading operation is generally performed by an employee of the electric utility who goes from house to house along a prescribed route and manually records all of the cumulative meter readings.
Although the manual reading of meters, as described above, has been used for many years, it presents serious difficulties and disadvantages under certain circumstances. For example, many utilities have experienced a problem in situations where one of their energy consumers has placed a fence, or other obstacle, in a position that prevents a meter reader from gaining access to the electric meter. Although fence-like obstacles are the clearest example of this type of situation, this type of difficulty can also be caused in locations where the electric meter is placed inside the residence and access to the residence is unavailable. For example, when many dwellings are built side-by-side, such as row house configurations, the electric meters are generally placed inside the dwellings and access to the meters depends on the presence of the home owner at the time the meter reader arrives.
One possible solution to the problem described above is to incorporate a power line carrier communication system in which the electric utility provides two-way communication devices at each electrical meter, within the consumer's residences, and uses a central station that communicates along the power line system to automatically read the kilowatthour values for each consumer. This type of system avoids the necessity of having a meter reader physically go to the house of the consumer to read the meter. However, for many electric utilities, the expense of this type of system cannot be justified by the relatively small percentage of meters that present the difficulties described above.
For an electric utility that has a large number of electric meters that are manually read and a relatively small percentage of those meters which are difficult to read because of various type of obstacles, it would be advantageous to provide a means for the meter reader to remotely read the meters at the residences where difficulties exist. It would be further advantageous if this type of remote meter reading apparatus did not require the central station transceiver, the repeaters, or the other equipment normally required in a complete power line carrier communication system.
The present invention incorporates the use of a portable remote meter reading apparatus which can be connected in signal communication with the power line which is in electrical communication with the residence at which the inaccessible electric meter is located. If the inaccessible consumer residence has been provided with a two-way communication device associated with its electric meter, the meter reader can utilize the present invention to command the two-way device to transmit its electric energy consumption information. When a meter reader uses the present invention, a fully equipped power line communication system is not required. Neither the central station transmitter nor the numerous repeaters and other transmission equipment are utilized by the present invention. All communications are between the meter at the consumer residence and the portable meter reading apparatus which is connected to the transmission line at a remote location that is not too distant from the inaccessible residence. In a typical application of the present invention, the portable remote meter reading apparatus is connected to the power line at the utility pole which is nearest the residence. Various alternative embodiments of the present invention utilize different connection techniques. For example, a female receptacle can be provided at the utility pole. This female receptacle would be connected in electrical communication with the customer's power line in order to provide a direct 120 volt connection between the female receptacle and secondary winding of the customer's distribution transformer. Alternatively, the present invention can be magnetically coupled to a ground wire connected to the distribution transformer. In situations where these two methods of connection are impractical, the present invention can be connected in electrical communication with a female receptacle at a neighboring residence. If the neighboring residence is connected to the same distribution transformer as the inaccessible meter, the present invention will provide power line communication between the portable remote meter reading apparatus and the inaccessible electric meter. Each of these alternative connections could utilize differently configured connection apparatus.
The present invention comprises a means for formulating a baseband signal that is representative of a manually entered command message. In a typical application of the present invention, a command message would contain operative instructions that command a remote meter to subsequently transmit information relating to its stored energy consumption information. Any one of a variety of different coding techniques can be used for formulate the baseband signal. The baseband signal comprises a plurality of bits that contain a numeric representation of the command message. The present invention also provides a means for modulating a carrier signal with the baseband signal. In a preferred embodiment of the present invention, a high frequency carrier signal is used. Although many different frequencies can be used, it has been found that a frequency of 12.5 kilohertz is suitable for this purpose. The modulation is accomplished by utilizing an exclusive-OR device having two imputs. One input is connected to a carrier generator that is capable of providing a continual stream of pulses at the prescribed frequency. The second input of the exclusive-OR device is connected to the source of the baseband signal. The modulated signal is then amplified for the purpose of injecting the modulated signal onto a conductor of a power line. For example, U.S. Pat. No. 4,467,314, which issued on Aug. 21, 1984 to Weikel et al., discloses a power line carrier communications system that includes a combination field configuration and test device that can be plugged into a load management terminal. This patent describes a terminal that is coupled to the power line through connection to the load management terminal for the purpose of generating a set of test commands which are transmitted over the power line for execution by the connected load management terminal. U.S. Pat. No. 4,065,763, which issued on Dec. 27, 1977 to Whyte et al., discloses a distribution network power line communication system that includes a coupling means for applying a carrier current communication signal to the polyphase primary distribution conductors with a proportional relationship between the signal voltages applied to the various conductors selected to provide a predetermined propagation mode.
The present invention also comprises a receiver circuit that is connectable in signal communication with the power line conductor. The receiver circuit contains a high pass filter that is capable of removing low frequency signals, such as the power transmission 60 Hz. waveform, from incoming messages received from the power line conductor. The receiver circuit also hard limits the incoming sinusoidal signals in order to provide a generally square, or rectangular, waveform. The hard limited signal is then sent to a demodulator that is connected in signal communication with the receiver circuit. The purpose of the demodulator is to demodulate the incoming sinusoidal signals and provide an incoming baseband signal which contains information representative of energy consumption that had been transmitted by a remote meter. Many different types of receiver circuits are known to those skilled in the art. For example, U.S. Pat. No. 4,382,248, which issued on May 3, 1983 to Pai, discloses a device for receiving communication signals carried by the phase conductors of a multi-phase power distribution network communication system. It includes a circuit for independently receiving each of the communication signals carried by the phase conductors. Although this patent specifically deals with receiving signals from three phases of a three phase power line system, it discusses known technology generally related to receiving signals from power line conductors.
Various types of demodulators are known to those skilled in the art of power line communication systems. For example, in a power line communication system that utilizes phase shift keyed (PSK) modulation techniques, a demodulator such as the one described in U.S. Pat. No. 4,311,964, which issued on Jan. 19, 1982 to Boykin, can be used. This patent describes an apparatus and method for coherent phase shift keyed demodulation of a binary phase shift keyed carrier. It sequentially processes plus and minus polarity samples of a plurality of carrier segments that occur within each carrier data symbol. The samples for each segment provide a binary coded signal for producing corresponding first and second relative phase angle vector signals. An improved coherent phase shift keyed demodulator is disclosed in U.S. Pat. No. 4,379,284, which issued on Apr. 5, 1983 to Boykin. This patent discloses an apparatus and method for coherent phase demodulation of a binary phase shift keyed carrier signal that is representative of the kinds of demodulators that can be used in conjunction with the present invention.
The present invention also comprises a means for translating the incoming baseband signal, after it is demodulated, into a value representative of energy consumption. Many different coding techniques can be used to numerically represent incoming information. The translating means of the present invention merely serves the function of converting the incoming digital signal into usable information. Part of this function is the conversion from pulse counts to kilowatthours or some other energy consumption value. Normally, this conversion can be accomplished by multiplying a pulse count value by a suitable conversion constant.
Electric meters that are capable of storing energy consumption data are typically configured with some type of pulse initiator or register dial encoding device. For example, U.S. Pat. No. 4,077,061, which issued on Feb. 28, 1978 to Johnston et al., discloses a metering system for electric utility power line measurements that includes voltage and current signal inputs that are sampled and converted to binary representations. It utilizes a sequence controller and calculator that provide programmed control for processing digital control and data signals and for producing digital calculations of electrical energy parameters from the binary representations of the instantaneous signal values. It utilizes memory registers to totalize and accumulate digitally calculated values for producing visual displays and output signals that corresponding to electrical energy parameters to be measured. U.S. Pat. No. 4,034,292, which issued on July 5, 1977 to McClelland, discloses an opto-electronic pulse initiator for producing meter data pulses from a meter having a rotating movement. A directionally oriented pattern containing at least two reflective surfaces is driven by the meter movement to sequentially activate first and second optical sensors. The optical sensors are connected to the inputs of a bistable logic circuit in order to produce predetermined mutually opposite binary logic states at the outputs of the bistable circuit with the logic states corresponding to a given direction of meter movement. Data pulse output channels are controlled by the bistable logic circuit to selectively produce meter data pulses for a predetermined direction of rotation of the meter movement. U.S. Pat. No. 4,439,764, which issued on Mar. 27, 1984 to York et al. discloses a remote meter reading system that includes a dial register encoder and a pulse encoder which are both coupled to the same rotary disc of an induction watthour meter. A first electronic data register stores the non-volatile dial register encoder output and a second electronic data register stores a value consisting of an initial value set by the dial register encoder at start-up time continuously augmented by the output of the pulse encoder since the start-up. Comparison and selective read-out of the two electronic data registers reduces erroneous meter reading outputs.
In situations where pulse initiators are utilized to measure energy consumption, the pulses generally represent revolutions of a meter disc. Although this type of value is directly representative of energy consumption, it must be multiplied by some predetermined constant value in order to convert it to readily usable units, such as kilowatthours. Therefore, the present invention incorporates programming means for translating the incoming baseband signal into a representative value in units which are easily understandable by a meter reader utilizing the present invention.
Field configuration terminals, such as the one described above in conjunction with the U.S. Pat. No. 4,467,314, are used in cooperation with a power line carrier communication system that involves an electric utility's entire distribution system. In such a system, the electric utility employs a central station that is capable of transmitting and receiving signals between many remote terminals located at consumers' residences. At various points within the transmission system, repeaters are used in order to amplify the signals transmitted between remote devices. When a field configuration terminal is used in conjunction with a specific load management terminal, or electric meter with transceiver capabilities, it is generally coupled directly to the terminal. In this way, the load management terminal can easily transmit and receive messages between it and the load management terminal, or meter, and this direct connection between the load management terminal (LMT) and the field configuration terminal (FCT) is also utilized to provide electrical power for the operation of the portable load management terminal. This convenience eliminates any need for using portable sources of electrical power. However, in order to achieve this convenience, the field configuration terminal must be coupled directly to the load management terminal, or meter, and this requires easy accessibility of the electrical meter. However, as discussed above, electric utilities experience many situations in which the meter is not accessible. Therefore, conventional field configuration terminals cannot be used because of the requirement of direct connection to the meter. The present invention avoids this disadvantage by providing a portable source of DC power for its meter reading apparatus. In a preferred embodiment of the present invention, this DC power is provided by a battery. The battery is used to provide power for the microprocessor, amplifier, display and other electronic components within the present invention.
In order to provide a solution for the problems described above, the present invention is portable so that it can be carried by a meter reader to a location that, although being remote from the meter to be read, permits the present invention to be connected to a conductor or ground wire of a power line system that is connected in signal communication with the meter. A portable source of direct current power is provided, generally in the form of a battery, in order to permit the present invention to be independent of the need for external power sources. A transmitter and a receiver are provided in the present invention to enable it to transmit and receive modulated signals, between it and a remote meter, along the power line conductor. A modulator and a demodulator are provided to accomplish conversion between baseband data messages and phase shift keyed modulated signals. A keyboard is provided to permit an operator to enter a command message into the present invention for subsequent formulation, into baseband data, and modulation prior to being injected onto the power line conductor. Receiver circuitry is provided to filter out low frequency waveforms from the incoming signal and to hard limit the incoming sinusoidal signal to provide a rectangular waveform to the demodulator of the present invention. After demodulation, the incoming signal is converted to usable units, such as kilowatthours, and displayed on a display for manual interpretation and recording of the information. The present invention is contained within a housing member which can be carried by the meter reader.